Question

1. The Phenomenon
A toy car launcher works as follows:

There is a compressible spring that is attached to a horizontal rail, on which a toy car can roll. The toy car can be pushed back against the spring, compressing it a certain distance. There is a little hook that holds the car against the compressed spring. When the hook is released, the spring pushes the car out of the launcher, down the horizontal track.

We want to ask some questions and make some predictions about different cars as they come out of the launcher. Upon close examination of this launcher, it is noted that the
spring is always compressed the same amount each time a car is loaded into the launcher.
The spring stays put inside the launcher as the car is pushed out.
2. What we want to know or predict

• Do all cars come out of the launcher with the same KE?
• Do all cars come out of the launcher with the same speed?
• If they don’t all have the same speed when they come out, what parameters cause the difference?
• What do we need to do to get our car to have a higher speed than our friend’s cars?

3. Create a Particular Model and use it to answer the questions
Plan what you need to do in your group and how you will proceed. Be systematic.
4. Suggestions:
• Use the Energy-Interaction Model and the Spring-Mass Model.
• Consider what energy systems are involved.
• Note: The car is in contact with the spring while it is compressed and separates
from the spring just as the spring reaches its equilibrium length. During the time
that the car and spring are together, they behave as a spring-mass system.
• To simplify the notation, use “d” for the distance the spring is compressed instead
of “∆x”.

HINT! Chose an interval that includes the moment when the spring and car are moving the fastest.

Answer 1